Method for welding pipe pieces made of thermoplastics

ABSTRACT

In a method for connecting pipe pieces of corrugated pipes to form a pipe, which is to be used in particular as a protection pipe for communication cables or light wave guides, external pipe segments are formed by appropriate cutting in the vicinity of the external pipe portions, which external pipe segments are inserted into recesses of welding sleeves. These welding sleeves comprise an outer ring and an inner ring, the inner ring not projecting radially beyond the inner pipe portions into the pipe. At least one of the rings is welded with the external pipe segments.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The invention relates to a method for welding together two pipe piecesof corrugated pipes.

BACKGROUND ART

In communication engineering mainly extruded solid pipes of polyethyleneare used, which are formed similar to gas or water pipes. These pipesare often mediaproof, i.e. liquidproof and gasproof, interconnected bywelding sleeves. As these pipes merely serve as a protective functionfor the cables received by the pipes, a so-called corrugated pipe couldaccomplish the same function at least more cost-effectively, as acorrugated pipe of this type can be manufactured with 40 to 60% lessmaterial with an equal annular rigidity based on its corrugated pipegeometry. In addition a corrugated pipe of this type is particularlysuitable for being used as a protection pipe in communicationengineering, as in the direction of its axis the cable takes its bearingin each case only on the internal pipe portions. The frictional forces,which occur when a cable or a light wave guide is drawn in suchcorrugated pipe, are by approximately 30% lower than with solid pipes,so that the length of the pipe pieces can be extended, which in turnleads to a reduction of the number of weld joints to be produced.

A welding of such corrugated pipes which is sure to be mediaproof is notknown up to this day, as the wall thicknesses thereof are relativelysmall.

SUMMARY OF THE INVENTION

It is an object of the invention to create a method of the generic type,by means of which a mediaproof connection of pipe pieces made ofcorrugated pipe is achieved.

This object is attained by providing two pipe pieces, which end with onefront surface each in a cylindrical external pipe segment, by pushingthe pipe pieces with their external pipe segments into annular recessesof a welding sleeve made of thermoplastics, the welding sleeve partiallysurrounding each external pipe segment, received by the sleeve, by meansof an outer ring and an inner ring, by plastifying the outer ring and/orthe inner ring on the one hand and the external pipe segment on theother hand by supplying electric current to the electric heatingelements at least in the region being adjacent to each other, bypressing during the plastifying process the pipe pieces towards eachother in the direction of the aligning axes until the annular recessesare filled at least substantially with the plastically deformed externalpipe segments and by switching off the electric current to connect theexternal pipe segments with the welding sleeve by cooling down. By themeasures according to the invention it is attained that a mechanicallyrigid and flat welding is produced between the external pipe portionsforming in each case a free end of each pipe piece and at least theouter ring or the inner ring of the welding sleeve. The inner ring ofthe welding sleeve does not project beyond the internal pipe portionsradially inwards into the corrugated pipe, so that also in the vicinityof the weld joint no obstruction is created for drawing in cables orlight wave guides. The partially inventive further improvements resultfrom the sub-claims.

Further features, advantages and details of the invention will becomeapparent from the ensuing description of examples of embodiment taken inconjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a corrugated pipe in a partial longitudinal cut,

FIG. 2 shows two pipe pieces formed of a corrugated pipe with a weldingsleeve before being joined,

FIG. 3 shows the pipe pieces and the welding sleeve according to FIG. 2after being pushed together at the start of heating and pressingtogether,

FIG. 4 shows the pipe pieces and the welding sleeve according to FIGS. 2and 3 at the end of heating and pressing together,

FIG. 5 shows a modified form of embodiment of a welding sleeve,

FIG. 6 shows a pipe piece with a welding sleeve and an electricresistance heating separated from the welding sleeve and

FIG. 7 shows a further form of embodiment of a welding sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 a partial section of a so-called corrugated pipe 1 isillustrated, i.e. of a pipe consisting of weldable plastics, for examplepolyethylene, polypropylene or the like. The corrugated pipe 1 comprisesa central longitudinal axis, concentrically to which the corrugated pipe1 is provided with corrugated portions 3. These comprise substantiallycircular cylindrical internal pipe portions 4 extending concentricallyto the axis 2 and substantially circular cylindrically formed externalpipe portions 5 also extending concentrically to the axis 2. An internalpipe portion 4 is connected with the adjacent external pipe portion 5via flanks 6 or 7, respectively, extending approximately radially to theaxis 2. Between an external pipe portion 5 and the flanks 6, 7 adjoiningthe latter a cavity 8 is formed, which is recessed--viewed from the axis2-- radially outwards in relation to the internal pipe portions 4. Theentire corrugated pipe 1 is continuously extruded as a hose and broughtinto the corrugated form on endlessly traveling calibrating devicesaccording to the so-called vacuum method or the so-called blowing methodor vacuum-blowing-method. Calibrating devices of this type are known forexample from British Patent 971 021.

As the pipes are produced endlessly, however, cannot be endlesslytransported, and as for the purpose of drawing in cables into such pipesthe length of a pipe piece is limited, the endless corrugated pipe 1must be divided. This is performed in the manner that by means of blades9 the corrugated pipe 1 is divided by cuts 10, 11 on both sides of aninner pipe portion 4 and of the flanks 6, 7 adjoining the portion, sothat--as can be seen from FIG. 2--the resulting pipe pieces 12, 13comprise on their free ends circular cylindrical external pipe segments5a with front surfaces 14, 15 extending radially to the axis,which--with the pipe pieces 12, 13 being arranged in alignment withanother--flush abut on each other, i.e. have an equal inside diameter dand an equal outside diameter D.

For the purpose of connecting two pipe pieces 12, 13 of this type, awelding sleeve 16 is provided in the example of embodiment according toFIGS. 2 to 4, which consists of an approximately cylindrical inner ring17 and of a likewise approximately cylindrical outer ring 18 surroundingthe inner ring 17 at a distance, which in turn are integrallyinterconnected by means of a middle web 19. The welding sleeve 16 ismade of the same material as the corrugated pipe 1, for example ofpolyethylene. Between the outer ring 18 and the inner ring 17 twoannular recesses 22, 23, open in the direction to the front faces 20,21, are formed, which recesses 22, 23 are formed slightly tapering inthe direction to the middle web 19. In the vicinity between the middleweb 19 and the respective front face 20 or 21 their largest diameter isD and their smallest diameter is d, so that when inserting the two pipepieces 12, 13 with their external pipe segments 5a comprising the frontsurfaces 14, 15 into the recesses 22, 23, the external pipe segments 5aarrive in the position shown in FIG. 3, in which the front surfaces 14,15 are still spaced away from the middle web 19.

In the outer ring 18 of the welding sleeve 16 an electric resistanceheating 24 is disposed, which can be connected with a power source viaconnection lines 25. When heating this resistance heating 24, thematerial of the outer ring 18 and in part the middle web 19 are melted.Furthermore, the regions, contacting the outer ring 18, of the elements,located in the recesses 22, 23, of the external pipe segments 5a areplastified. The inner ring 17 of the welding sleeve 16, however, is notplastified. The two pipe pieces 12, 13 being pressed in directiontowards each other in accordance with the arrows 26, 27 during theheating and plastifying or melting process, the external pipe segments5a located in the recesses 22, 23 are fully pressed into these recesses22, 23 and on this occasion are being deformed in such a manner thatthey penetrate into the recesses 22, 23 over the full length a of thelatter, until their front surfaces 14, 15--now having changedshape--abut on the middle web 19 and are also welded with the latter, ascan be seen from FIG. 4. From FIG. 4 it can also be seen that theexternal pipe segments 5a welded together with the welding sleeve 16comprise a slightly upset portion 28 outside of the welding sleeve 16 atthe transition to the respective adjacent flank 6 or 7, respectively.After the connection shown in FIG. 4 of the two pipe pieces 12, 13 withthe welding sleeve 16 has been attained, current is cut off so that theplastified plastics solidify in this position, by means of which amediaproof, i.e. a liquidproof and gasproof welding of the two pipepieces 12, 13 is achieved. As the inner ring 17 of the welding sleeve 16is not heated, it is not being deformed under the welding pressure inthe direction of the arrows 26, 27. As can be seen in particular fromFIG. 4, the inner ring 17 does not project radially inwards beyond theinternal pipe portion 4.

The welding sleeve 16' shown in FIG. 5 differs from the sleeve shown inFIGS. 2 to 4 only in an annular stiffening inlay 29, embedded allover inthe inner ring 17' and made for example of metal, being arranged in theinner ring 17', by means of which stiffening inlay 29 the stiffness ofthe inner ring 17' and thus of the welding sleeve 16' in all is enhancedduring the temperature load, i.e. during welding. Compared to theembodiment according to FIGS. 2 to 4 this stiffness is higher, althoughin that case also a considerable stiffness is maintained based on thenonheating of the inner ring 17.

In the embodiment according to FIG. 6 the welding sleeve 16" is notprovided with an electric resistance heating, i.e. also its outer ring18" consists only of the material of the corrugated pipe 1. An electricresistance heating 30 is provided for each pipe piece, of which only onepipe piece 12 is illustrated. This electric resistance heating 30 isformed by a heater band 31 consisting of resistance wires, which heaterband 31 is U-shaped bent, as can be seen from FIG. 6. In this manner itcan also be pushed over the front surface 14 of the pipe piece 12 ontoits external pipe segment 5a. This external pipe segment 5a togetherwith the electric resistance heating 30 is pushed into the annularrecess 22" of the welding sleeve 16", the outer ring 18" of whichcomprises a cutout 32 for the connection lines 33 of the resistanceheating 30. As can be seen from FIG. 6, a corresponding cutout 32 isassociated to the other annular recess 23", too. The largest diameter D"and the smallest associated diameter d" each time in the middle regionof each recess 22" or 23", respectively, is a little larger or a littlesmaller, respectively, than the corresponding diameter D or d,respectively, of the external pipe segment 5a, as the latter in additionis enlarged or reduced, respectively, by the electric resistance heating30. With this embodiment the surface regions, resting on each other, ofthe external pipe segment 5a and of the wall portions, delimiting therecess 22" or 23", respectively, of the welding sleeve 16" are directlyplastified by the resistance heating 30. The stiffness of the weldingsleeve 16" is remained in this case by the external region of the outerring 18" and the internal region of the inner ring 17" being not or onlyslightly heated and thus being not plastified.

It may occur that a pipe, which consists of pipe pieces 12, 13, whichare interconnected by a welding sleeve 16 or 16' or 16", is inserted orinstalled at places, where the outer ring 18, 18" of the welding sleeve16, 16', 16" must not project beyond the corrugated portions 3. In sucha case this outer ring 18 or 18", respectively, must be peeled after thewelding process. With the object of nevertheless achieving asatisfactory welding in such a case, welding may be effected accordingto FIG. 6. As in this case also the inner ring 17" is welded with theexternal pipe segment 5a, the outer ring 18" can be peeled after thewelding is produced. However, also a welding sleeve 16"' according toFIG. 7 can be used, which differs from the welding sleeve 16 accordingto FIGS. 2 to 4 only in the electric resistance heating 24"' beingformed in the inner ring 17"', whereas no such heating is arranged inthe outer ring 18"'. In this case the outer ring 18"' assumes the taskto confer the necessary stiffness to the welding sleeve 16"' during thewelding process. This outer ring 18"' is then peeled after the weldingprocess.

What is claimed is:
 1. A method for welding together two pipe pieces ofcorrugated pipes comprising:providing a first thermoplastic pipe pieceand a second thermoplastic pipe piece, each pipe comprising corrugatedportions with internal pipe portions and external pipe portionsalternately succeeding in the direction of a central longitudinal axisand with substantially radial flanks interconnecting the said twoportions and said first pipe piece ending in a first front surface of acylindrical external pipe segment, and said second pipe piece ending ina second front surface of a cylindrical external pipe segment, providinga thermoplastic welding sleeve comprising an outer ring and an innerring, which outer ring and which inner ring are arranged concentricallyto said central longitudinal axis and which said outer ring and whichsaid inner ring define a first annular recess and a second annularrecess, which two recesses are separated by a middle web from eachother, which middle web interconnects said outer ring and said innerring, and wherein said inner ring radially to said central longitudinalaxis is located exclusively between said external pipe segments and saidinternal pipe portions of said pipe pieces, providing electrical heatingelements adjacent to at least one of said outer ring and said innerring, pushing said external pipe segment of said first pipe piece intosaid first annular recess of said welding sleeve and said external pipesegment of said second pipe piece into said second annular recess ofsaid welding sleeve, plastifying at least one of said outer ring andsaid inner ring and said external pipe segments of said first and secondpipe pieces by actuating the electric resistance heating elements withelectric current, pressing said two pipe pieces towards each other whiledeforming said external pipe segments until said external pipe segmentsfill at least substantially said two annular recesses and switching offthe electric current and cooling said welding sleeve and said externalpipe segments to connect said external pipe segments with said weldingsleeve.
 2. A method according to claim 1, wherein said electric heatingelement consists of an electric resistant heating element arranged insaid outer ring.
 3. A method according to claim 1, wherein said electricheating element consists of an electric resistance heating elementarranged in said inner ring.
 4. A method according to claim 1, whereinsaid welding sleeve is provided with an inner ring which has astiffening inlay.
 5. A method according to claim 1, wherein an electricresistance heating element separated from the welding sleeve isprovided, which electric resistance heating element is placed on saidexternal pipe segments to be inserted into the respective recess.
 6. Amethod according to claim 1, wherein said annular recesses slightlytaper from front faces of said welding sleeve towards said middle web ofsaid welding sleeve.